Pacemaker system with automatic event-programmed switching between unipolar and bipolar operation

ABSTRACT

A pacemaker system incorporates an implantable pacemaker and a plurality of electrodes, electrodes preferably being on a pacing lead for a single chamber pacemaker, or a pair of such leads for a dual chamber pacemaker. Programmable connection means are provided for connecting the pacemaker output to a selected combination of lead electrodes, the selection being changed during each pacer cycle to optimize the choice of unipolar and bipolar operation for given pacemaker events. In one mode, the system employs bipolar QRS sensing and unipolar pacing and T-wave sensing. In another mode, the system employs bipolar QRS sensing and pacing, and unipolar T-wave sensing.

BACKGROUND OF THE INVENTION

This invention lies in the area of cardiac pacers and the method ofoperation of same, with programmed means for varying pacemaker operationand, in particular, pacemaker systems and other implantable systems withmicroprocessor control for switching between unipolar and bipolaroperation in accordance with programmed events such as sensing ofpatient signals and stimulus delivery.

In the field of cardiac pacemakers, there is a need to provide anefficient electrode system for the operations of delivery of stimuluspulses and sensing patient heartbeat signals. In a conventional singlechamber demand pacemaker, of the demand type, the electrode system mustprovide for efficient delivery of ventricular stimulus signals, and alsoprovide efficient pick up of natural QRS signals. In dual chamberpacemakers, there is additionally a need to be able to sense atrialsignals, and to deliver atrial stimulus pulses from the pacemaker. Inanother type of pacemaker, as set forth in U.S. Pat. No. 4,228,803,assigned to the same assignee, there is a need to sense T-waves.

Generally there are two types of electrode systems which are used incardiac pacing. In the bipolar system of operation, two electrodes arepositioned near the tip of a lead which is placed into the heart, theelectrodes typically being rings which conduct the stimulus pulse andsense natural cardiac signals. In a unipolar electrode arrangement, asingle electrode is placed on the lead, preferrably out or near the tip,and an indifferent electrode is utilized at a location remote from theelectrode tip. Most typically, in unipolar, or monopolar arrangements,the indifferent electrode is a portion of the pacemaker housing, whichis a convenient way of obtaining a large surface indifferent electrode.Alternately, the indifferent electrode may be positioned on the leaditself, at a point proximal to the tip, as is known in the art.

The pacemaker industry has not resolved, and indeed cannot resolve thequestion of whether unipolar or bipolar operation is generallypreferrable. Some physicians adhere to one or the other modes ofoperation, having their own reasons for doing so. Most pacemakermanufacturers have provided pacing systems for operation in each of themodes, such that the physician can choose a unipolar or a bipolarsystem. Bipolar leads and systems have the advantages of reduced pick upof electromagnetic interference, and they avoid the problem of unipolarsystems wherein the pectoral muscle can be inadvertantly excited.Unipolar systems are generally recognized to have the advantage ofbetter sensitivity for sensing heart signals, and to have reducedpolarization problems due to the relatively large indifferent electrodeand the relatively small lead electrode. In special applications, suchas searching for an evoked response signal (QRS wave) following deliveryof a stimulus pulse, or in measuring T-waves, the unipolar system isdefinitely preferable. There could be a problem if, in a bipolar system,the heart muscle is captured at both electrodes, in which case thesensed T-wave and QRS wave would be simply the difference of the twosignals and would be very small.

In view of the above, it is seen that there is a need to provideincreased flexibility, by which the pacer system can utilize theadvantages of each of the bipolar and unipolar modes of operation forthe particular events that are taking place. Thus, there is a need for asystem which automatically switches between unipolar and bipolar formsof operation, the switching being programmed for optimal operation ofthe different pacer events which take place during each pacing cycle.The desirability for switching applies to both single chamber and dualchamber pacing systems. In dual chamber systems, it may be desirable,for example, to have bipolar operation in the atrium to reduce the needfor blanking following delivery of the ventricular stimulus, while atthe same time having a unipolar electrode arrangement for sensing Pwaves. Generally, considerations for unipolar and bipolar sensing varyat different times in the pacing cycle, dependent upon the nextanticipated event.

While this invention is described in terms of switching between unipolarand bipolar operation in a pacemaker system, it is to be understood thatit generally applies to optimized switching of various electrodesystems, for pacemakers and other types of devices for deliveringstimuli to a patient and/or sensing patient signals. For example,electrode configurations may be used which are not termed unipolar orbipolar, as those terms are understood in the pacemaker art, but whichelectrode configurations are changed during cycles of operation of thesystem.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a stimulus delivery systemhaving an implantable device and an electrode configuration with aplurality of electrodes, and a controllable connection circuit forconnecting the electrodes to the stimulus/device in variousconfigurations, the circuit being switchable during each device cycle soas to optimize the electrode configuration in terms of system events.

It is another object of this invention to provide a pacing system withmicroprocessor control for changing the system operation betweenunipolar and bipolar operation within each pacing cycle, in accordancewith programmed events.

It is another object of this invention to provide an implantable devicesystem with programmed means for automatically changing the electrodeconfiguration in accordance with the programmed system operation.

It is a further object of this invention to provide a pacemaker systemwith program means for cyclically switching the pacemaker sensing meansand electrode configuration, to optimize sensing of patient cardiacsignals.

It is a further object of this invention to provide a pacemaker systemwith means for automatically accumulating data corresponding to systemoperation, and for automatically switching the system electrodeconfiguration in accordance with such accumulated patient data.

In accordance with the above objects, there is provided a pacemakersystem having an implantable pacemaker with means for deliveringstimulus pulses and means for sensin patient signals, the pacemakerbeing in programmable connection with an electrode configuration havinga plurality of electrodes, and controllable means for switching theelectrodes connected to the pacemaker so as to provide alternatelyunipolar and bipolar operation. The pacemaker system preferably containsmicroprocessor control for cyclically programming switching betweenunipolar and bipolar operation to optimize the electrode configurationfor predetermined pacing events such as stimulus delivery and sensing ofgiven patient heart signals. In another embodiment, the pacemakermonitors one or more system events over one or more pacemaker cycles,and automatically selects an optimum electrode configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing the main components of a demandpacemaker system in accordance with this invention.

FIG. 1B is a block diagram showing the main components of a dual chamberpacemaker in accordance with this invention.

FIG. 1C is a schematic illustration of a pacemaker and lead,illustrating placement of electrodes to achieve bipolar and unipolarmodes of operation.

FIGS. 2A and 2B present a flow diagram of a programmable pacemakerutilizing the subject invention.

FIG. 3 is a flow diagram of a routine for switching the electrodeconfiguration as a function of performance monitored over a plurality ofcycles of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1A, a pacemaker is shown in a casing, or housing30. An indifferent electrode 43, as also shown in FIG. 1C, forms aportion of the outside surface of the casing, as is conventional in thepacemaker art. The pacemaker contains circuitry, as shown at block 32,for generating and delivering stimulus pulses, or stimulus signals, andcircuitry as shown at block 34 for sensing patient heart signals, e.g.QRS and T waves, or atrial P waves. A microprocessor control,incorporating a microprocessor chip or chips as well as associatedcontrol circuitry, is shown at block 36. Communications as indicatedbetween the microprocessor control and the stimulus and sense circuitryenable overall control of the pacer, in a known manner. A power sourceas shown at 38 provides a voltage V_(B) which is applied to all of thecircuitry. As illustrated, the negative side of the power source isconnected to the circuitry, and the positive side is connected to thesystem ground. All of these features are conventional and well known inthe art. See, for example, European Patent Application No. 81108940.8.

The output of the stimulus amplifier circuitry, as well as the input tothe sense circuitry are tied in common and fed through the pacer housingand connected through a conventional lead to a first electrode 41,designated electrode 1 in FIG. 1A. This electrode is typically locatedat the end of the lead, as illustrated in FIG. 1C. A bipolar lead ofconventional design carries a second electrode, suitably a ringpositioned proximally to the distal first electrode, and electricallyconnected by a conductor running the length of the lead. A thirdelectrode is suitably provided by a plate 43 which forms a portion orsubstantially all of the pacemaker can, or housing, as also illustratedin FIG. 1C.

In the system of this invention, an electronically controlled switch 40is provided which operates to switch either the second electrode or theindifferent electrode to the system ground. When the switch connects thesecond electrode (42) to system ground, then the two ring electrodes asseen in FIG. 1C are connected to the pacemaker, and bipolar systemoperation is achieved. With this mode of connection, a stimulus pulsemay be delivered with the voltage difference being directly across thetwo ring electrodes 41, 42. When the switch 40 is switched so that theindifferent electrode 43 is connected to system ground, then ringelectrode 42 is not connected to the pacemaker, and unipolar operationis achieved. In unipolar operation, a delivered stimulus pulse presentsa voltage between the small electrode 41 at the tip of the lead, and thelarge electrode 43 on the pacemaker casing. As is known in the art, theindifferent electrode may be positioned other than on the pacemakerhousing, and could be positioned as shown at 43' in FIG. 1C, farproximal on the lead itself.

The operation of switch 40, as illustrated in FIG. 1A, is under controlof the microprocessor control circuitry 36. Switch 40 may be any wellknown semiconductor switch, such as is easily provided in the art, theswitching operation being under the control of a conventionalmicroprocessor or other analog or digital controller. In the preferredembodiment of microprocessor control, the switch may be accuratelycontrolled at programmed intervals of each pacing cycle, as illustratedin FIGS. 2A and 2B below. It is to be understood that the switch controlmay take any conventional design form, including the use of analogcircuitry in a well known manner.

Referring to FIG. 1B, there is shown a block diagram illustrating a moregeneral system encompassed by this invention, as applied as a dualchamber pacemaker. Microprocessor control circuitry 36 is shown intwo-way communication with pacer stimulus and sense circuits as shown inblock 45, and switch means as shown in block 46. The switch meansprovide the function of connecting a plurality of electrodes, indifferent combinations, to the pacer stimulus and sense circuits. Asillustrated, five electrodes may be used, two atrial electrodes 47, twoventricular electrodes 48, and an indifferent electrode 43. It is to beunderstood that in the general application of this invention, forpacemaker systems or other similar implantable systems, the number ofelectrodes that may be utilized is unlimited. The invention covers theautomatic switching of different electrode configurations duringrepetitive cycles, the electrode configurations being chosen for usewith one or more predetermined programmed events. In the pacemakersystem embodiment, the programmed events include sensing of differentnatural and/or evoked heart signals, and delivery of stimulus pulses toone or more heart locations. As illustrated in FIG. 1B, the switch meansmay also controllably connect to an extra sensor 52, which may be anadditional cardiac electrode or a sensor for sensing another patientparameter.

Referring now to FIGS. 2A and 2B, there is illustrated a flow diagramcovering a cycle of pacer operation. The flow diagram is repeatedcontinuously each pacer cycle.

Referring to FIG. 2A, there is illustrated an example of amicroprocessor controlled cardiac pacemaker system which changes itselectrode configuration, as well as filter characteristics, within thepacer cycle. The program, as illustrated, is for a ventricular demandpacer, and starts at a time just after the time out of the pacerrefractory period. At block 207, the filter of the input amplifier,connected to receive a patient cardiac signal, is set to an appropriateQRS setting, i.e., set to an appropriate bandpass for detecting apatient QRS signal. At block 208, a bipolar connection is set, forbipolar QRS sensing. At block 233, the microprocessor enables sensingthrough the input amplifier, and, for example, sets the sensitivity at 2mV. At block 234, the microprocessor is stopped to await either timeoutor a sensed QRS. When either of these events occurs, the microprocessorpicks up at block 236 and records the time T of the last cycle, and thendetermines whether a timeout has occurred, at block 238.

If a timeout has occurred, meaning there has been no natural patientbeat, the program block branches to the right. In preparation forgenerating the stimulus, the filter of the input amplifier is first setto a high frequency characteristic, at block 239, in order to quicklydamp out any artifacts produced by the generated stimulus. If unipolarpacing is desired, a unipolar connection is also set at this point.Thereafter the pacer timer is set to zero at block 240, and the stimulusis generated at block 241. Bookkeeping type operations are done at242-245 and 201; an end-of-life (EOL) test may be done at 202-204, andat 205 the program exits either to the "on-demand" path of FIG. 2B, orto a fixed rate path. If the "NO" branch is taken at block 238, nostimulus is generated, and bookkeeping functions 250-252 are carriedout.

Referring to FIG. 2B, the program continues after the stimulus deliveryprovided in FIG. 2A. The program as illustrated provides for controllingthe rate of delivered stimulus pulses as a function of stimulus T timeintervals. A time delay is introduced at block 260, corresponding to thedelay between the stimulus and the start of evoked response sensing. Thesense amplifier is disabled at block 261, and the microprocessor isstopped to wait for the delay T₁. At block 262, the microprocessordetermines whether the timer has timed out. If yes, and the last cyclewas a pace cycle, as determined at 210, the pacer control branches tothe right. At block 263, a switchable filter such as disclosed in U.S.application Ser. No. 475,024 is set to the evoked QRS setting, i.e., toa filter characteristic optimally designed to detect an evoked QRS. Aperiod T2 is put into the timer at 264, during which the pacer looks forthe evoked response. At block 265, the electrodes are connected forunipolar operation, e.g., switch 40 is set to connect the indifferentelectrode to ground, leaving ring electrode 42 unconnected. The senseamplifier is enabled at block 266, for example with a sensitivity of 8mV. At block 268, it is determined whether the timer has timed out. Ifno, meaning that an evoked response was detected, the ERS flag is set atblock 271. If yes, meaning that there was no evoked response, thenon-ERS flag is set at 270. Following this, at block 273, themicroprocessor goes through an output processing subroutine, to changethe stimulus magnitude if required to achieve heart capture. At block274, the filter characteristic of the input amplifier is modified to acharacteristic adapted for detecting the T wave portion of the heartsignal. Following this, at block 276, a time interval TPT correspondingto the T wave time is set into the timer, and at block 277 the senseamplifier is enabled at a sensitivity of, for example, 1 mV. Themicroprocessor is stopped at 280, and is started again at 281 either bya sensed T wave or by timing out. If it is not timed out, meaning that aT wave was sensed, the time of this T wave in relation of the deliveredpulse stimulus is stored at 283. At block 284, the microprocessor goesthrough a rate subprocessing routine to change the pacer rate, as setforth in U.S. Pat. No. 4,228,803. If, at block 210, it is determinedthat the last cycle was ended by a sensed natural QRS, the programbranches to block 226, where the refractory interval is established bysetting the timer to Ter. The sense amplifier is disabled at block 277,and the microprocessor is stopped to await the time out of therefractory period as shown at block 228.

As illustrated, FIGS. 2A and 2B show an example of cyclic bipolaroperation for sensing QRS and for stimulation, and monopolar (unipolar)T wave sensing. Unipolar pacing can be achieved by setting the unipolarconnection after QRS sensing (or time out) and before delivery of thestimulus pulse. Dual chamber operation employs additional such switchingsteps in accordance with desired electrode modes for atrial sensing andstimulating.

Referring to FIG. 3, there is illustrated a routine which can beutilized in a pacemaker or other implantable device, for monitoringperformance and reprogramming a desired switch connection as a functionof monitored performance. The reprogramming can be done with respect tocyclical switching, e.g., for the embodiment of FIGS. 2A and 2B periodicsignal sensing can be changed from bipolar to unipolar, or vice versa.Alternately, the reprogramming can be done on a permanent or fixedbasis, e.g., the pacemaker may switch from fixed unipolar operation tofixed bipolar, or vice versa.

The program of FIG. 3 illustrates monitoring a sensed heartbeat signalto obtain a measure of whether the sensing operation would be performedbetter in the unipolar or bipolar mode. The amplitude of a receivedinput signal, e.g. QRS or P wave, is stored at block 285. At block 286,a new sum designated A SUM is accumulated by adding the just receivedamplitude A to the prior sum. At block 287, the number of iterations Iis incremented by 1. In the illustration, the routine iterates 10 timesin order to accumulate a sum, but it is to be understood that one ormore measurements can be made, and that the number of iterations is amatter of choice. At block 288, it is determined whether I is less than10. If yes, more cycles are to be measured, and the routine branchesdirectly to the end. If no, meaning that 10 measurements have now beenaccumulated, the program proceeds to block 289 where it is determinedwhether A SUM is less than the prior, or old A SUM. If no, meaning thatA SUM has increased, reflecting improved performance, the routinebranches to block 292. If yes, meaning that performance hasdeteriorated, the routine first performs the operation at block 290 ofchanging the switch connection, i.e., changing the electrode mode forthe sensing activity from bipolar to unipolar, or vice versa.Thereafter, at block 292, the microprocessor stores the accumulated ASUM as A SUM OLD. At block 294, the present values of A SUM and I areset to zero, and the program exists.

The subroutine of FIG. 3 may be run continuously initiated periodicallyby a counter in the pacemaker; or initiated by an external programsignal. It is presented as an illustration of utilizingdevice-accumulated information to make the choice of mode setting. Whilethe illustration given relates to sensing a received heart signal,patient information relative to stimulus delivery can likewise beaccumulated. With evoked response sensing, a patient threshold can bedetermined by known means, and threshold compared for unipolar versusbipolar stimulus delivery. It is to be understood that the routine forcyclic switching between unipolar and bipolar operation can bere-programmed from an external source, by means well known in the art.

We claim:
 1. Pacemaker apparatus having an implantable pacemaker, saidpacemaker having stimulus means for generating stimulus pulses, sensingmeans for sensing heart signals, and cyclic means for controlling saidpacemaker to carry out cyclic operation, a lead with at least two spacedlead electrodes thereon, and an indifferent electrode,comprising:connection means for controllably connecting said sensingmeans and said stimulus means to respective selected ones of a pluralityof combinations of said lead electrodes and said indifferent electrode;selection means for selecting respective first and second ones of saidcombinations for sensing of respective heart signals at different timesduring a cycle of pacemaker operation; and control means for controllingsaid connection means in accordance with said selected combinations 2.The apparatus as described in claim 1, wherein a first of saidcombinations comprises one of said lead electrodes and said indifferentelectrode, and a second of said combinations comprises two of said leadelectrodes, thereby providing selection between unipolar and bipolaroperation.
 3. The apparatus as described in claim 2, wherein saidpacemaker is housed in a housing, said housing having at least a portionof the outside of which comprises said indifferent electrode.
 4. Theapparatus as described in claim 1, said sensing means having firstsensing means for sensing a first selected heartbeat signal and secondsensing means for sensing a second selected heartbeat signal, andwherein said selection means has first selection means for selectingsaid unipolar connection for sensing of said first selected heartbeatsignal once each pacing cycle, and second selection means for selectingsaid bipolar connection for sensing of said second selected heartbeatsignal once each cycle.
 5. The apparatus as described in claim 4,wherein said first sensing means senses T waves.
 6. The apparatus asdescribed in claim 5, wherein said second sensing means senses QRSsignals.
 7. The apparatus as described in claim 1, said sensing meanshaving QRS means for sensing QRS signals and T wave sensing means forsensing T waves, and wherein said selection means selects said unipolarconnection each pacing cycle for T wave sensing and delivery of astimulus pulse, and selects said bipolar connection each cycle for QRSsensing.
 8. The apparatus as described in claim 1, wherein saidselection means further comprises means for selecting one of saidcombinations for delivery of a stimulus pulse during said cycle. 9.Pacemaker apparatus for delivering stimulus pulses, said apparatushaving pacing means for generating said stimulus pulses and sensingmeans for sensing patient heartbeat signals, a housing which houses atleast said pacing means, at least a portion of which housing comprisesan indifferent electrode, and a lead having at least two electrodes,said pacing means having program means for carrying out cyclicaloperation, characterized further byconnecting means for selectivelyconnecting said pacing means to two of said lead electrodes for bipolaroperation or to said indifferent electrode and one of said leadelectrodes for unipolar operation, first control means operable eachpacemaker cycle to control said connection means to make a selectedconnection during delivery of a stimulus pulse, and second control meansoperable twice each pacemaker cycle to control said connection means tomake predetermined selected connections for sensing of patient heartbeatsignals at two respective times during said each cycle.
 10. Theapparatus as described in claim 9, wherein said connection meanscomprises a switching circuit which is controllable to connect saidpacing means alternately to one of said lead electrodes or to saidindifferent electrode.
 11. The apparatus as described in claim 9,further characterized by having a second lead having at least twoelectrodes and second connection means for connecting said pacing meansto said second lead for unipolar or bipolar operation.
 12. Pacemakerapparatus for delivering stimulus pulses, said apparatus having pacingmeans for generating said stimulus pulses and sensing means for sensingpatient heartbeat signals, a housing which houses at least said pacingmeans, at least a portion of which housing comprises an indifferentelectrode, and a lead having at least two electrodes, said pacing meanshaving program means for carrying out cyclical operation, characterizedfurther byconnection means for selectively connecting said pacing meansto two of said lead electrodes for bipolar operation or to saidindifferent electrode and one of said lead electrodes for unipolaroperation, monitoring means for monitoring the occurrence and absence ofoccurrence of at least one said sensed heartbeat signal during eachpacemaker cycle, and control means for controlling said connection meansduring each said cycle as a function of said monitoring.
 13. Theapparatus as described in claim 12, wherein said sensing means has QRStiming means for timing out a QRS period for sensing a QRS signal, saidcontrol means controlling said connection means for bipolar operationduring said QRS period and for unipolar operation at about the end ofsaid period.
 14. Pacemaker apparatus having a pacemaker with programmeans for controlling repetitive cycles of pacemaker operation and aplurality of electrodes for delivering stimulus pulses and sensing heartactivity, said pacemaker comprising:connection means for controllablyconnecting said pacemaker to a selected combination of said electrodes;determining means for determining pacemaker data over a plurality ofsaid cycles, and control means for controlling said connection means asa function of said determined pacemaker data.
 15. The apparatus asdescribed in claim 8, wherein said determining means comprises means forcyclically sensing heart signals and for generating valuesrepresentative of a feature of said sensed signals, means foraccumulating said values over a predetermined number of cycles to derivesummation values, and means for comparing respective summation values.